This invention relates to lamps in general and, in particular, to a lamp assembly capable of throwing a beam of light in a preassigned direction at a considerable angle to its optical axis. The lamp assembly in accordance with the invention lends itself to use as, typically, a supplemental high mounted stop lamp on motor vehicles.
As the name implies, supplemental high mounted stop lamps are additional lamps of a vehicular stop lamp system that are mounted high, and typically interiorly of the vehicle rear window, for giving a steady warning light through intervening vehicles to operators of following vehicles. Some motor vehicles to say, passenger cars, in particular, have their rear windows arranged a considerable angle out of the perpendicular for hydrodynamic reasons or from design considerations. In mounting supplemental stop lamps interiorly on such a steeply slanting rear window, it is desired that their sealing plane be parallel to the window. So mounted, the stop lamps must of course emit beams of light at a considerable angle to their seating plane.
A typical conventional supplemental stop lamp intended for such use includes a lamp body to be mounted horizontally with its sloping front end held interiorly against the vehicle rear window. The lamp body has at its rear end a praaboiloidal reflector for producing parallel rays of light from a bulb positioned at its focus. Mounted at the open front end of the lamp body is a generally planar lens which is set parallel to the vehicle rear window and so at a great angle to the lamp axis. The lens has a multiplicity of diverging lens elements formed thereon for diverging the parallel light rays both laterally and vertically, so that the resulting beam may reach a sufficiently wide area to the rear of the vehicle.
The prior art stop lamp of the foregoing construction must have a vertical dimension, transverse to its optical axis, of not less than a prescribed limit to give a required degree of beam intensity. Because of the slanting rear window, however, the desired vertical dimension is gained only by correspondingly increasing the lens dimension in the height direction of the lamp parallel to the window. This in turn requires an increase in the axial dimension of the lamp body, resulting in the inconvenient bulging of the lamp body toward the interior of the vehicle.
In addition to such mechanical or dimensional difficulties, the prior art stop lamp has an optical problem as well. The parallel rays of light produced by the paraboiloidal reflector are rendered divergent as aforesaid by the multiple lens elements that are molded in one piece as the generally planar lens member at the slanting front end of the lamp body. The lens member is mounted at such an angle to the optical axis of the lamp assembly that no negligible proportion of the parallel light rays from the reflector is reflected away therefrom, instead of transversing same thereby to be diverged for beam coverage over a greater area. No effective measure is known to the present applicant that has heretofore been taken for the avoidance of such waste of light energy in the stop lamp of the type in question.